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Double-mixed-refrigerant liquefying system applied to base-load type natural gas liquefying plant

A technology of mixing refrigerant and natural gas, applied in the field of natural gas liquefaction, can solve the problems of low adaptability of high-pressure gas source, complex process structure, short service life, etc., and achieve the effect of strong adaptability, simple process structure and long service life

Active Publication Date: 2013-08-07
CHINA NAT OFFSHORE OIL CORP +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0002] At present, the common domestic natural gas liquefaction technology is mostly nitrogen expansion and single-stage mixed refrigerant cycle refrigeration process, which can only be applied to small-scale LNG plants, usually using plate-fin heat exchangers, which are not highly adaptable to high-pressure gas sources, and short service life
The liquefaction process used in large-scale natural gas liquefaction plants in foreign countries mostly adopts propane precooling mixed refrigerant liquefaction process (C3 / MR) or dual mixed refrigerant refrigeration liquefaction process (DMR). The former (C3 / MR) precooling heat exchanger usually uses Floating head heat exchangers require a large number of heat exchangers for multi-stream heat exchange, resulting in a complex process structure; the latter (DMR) precooling and cryogenic heat exchangers mostly use two-stage refrigeration heat exchange, low thermal efficiency
In addition, the foreign DMR process usually uses BOG cryogenic refrigerant for heat exchange, and the cooled cryogenic refrigerant is throttled and then exchanged heat with raw material gas, which is more efficient than the heat exchange method using BOG directly with raw material gas Low

Method used

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  • Double-mixed-refrigerant liquefying system applied to base-load type natural gas liquefying plant
  • Double-mixed-refrigerant liquefying system applied to base-load type natural gas liquefying plant

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0021] Such as figure 1 As shown, the dual mixed refrigerant liquefaction system provided by the present invention includes a precooling heat exchanger 1, a liquefaction heat exchanger 2, a precooling mixed refrigerant refrigeration cycle mechanism and a liquefied mixed refrigerant refrigeration cycle mechanism; the precooling heat exchanger 1 and the liquefaction heat exchanger 2 are both coiled tube heat exchangers. The pre-cooling mixed refrigerant refrigeration cycle mechanism includes a buffer tank I3 connected in sequence, a first-stage pre-cooling refrigerant compressor 4, a pre-cooling refrigerant cooler I5, a gas-liquid separator I6, and a second-stage pre-cooling refrigerant compressor 7 , pre-cooling refrigerant cooler II8 and gas-liquid separator II9; the buffer tank I3 is connected to the bottom of the pre-cooling heat exchanger 1; the liquid phase outlet of the gas-liquid separator I6 is connected to the bottom of the pre-cooling heat exchanger 1 ; The liquid ph...

Embodiment 2

[0027] Using the liquefaction system in Example 1 to liquefy the raw material gas of the third typical LNG component in GB19204,

[0028] The feed gas components are 87.2% methane, 8.61% ethane, 2.74% propane, 0.65% butane, 0.42% isobutane, 0.02% pentane and 0.36% nitrogen; The composition of the agent.

[0029] The specific steps are basically the same as in Example 1, because the heavy components in the raw gas components increase, so the outlet of the precooling mixed refrigerant refrigeration cycle mechanism needs to remove the heavy hydrocarbons condensed in the raw gas, after calculation, the precooling 1. The distribution ratio of mixed refrigerant components in the liquefaction unit needs to be optimized.

[0030] The amount of heavy hydrocarbons removed from the feed gas by the precooling mixed refrigerant refrigeration cycle mechanism is 20t / h. All the other parameters in the flow process are the same as Example 1, and the product liquefaction rate obtained is 91%....

Embodiment 3

[0032] Use the liquefaction system in Example 1 to liquefy a certain component of raw natural gas in a cold sea area, and the temperature of the seawater used for cooling is 13°C, such as figure 2 As shown, because the temperature of the refrigerant medium is relatively low, a raw gas cooler 19 is added to the raw gas at the inlet of the precooling heat exchanger 1 to cool the raw gas. In addition, the cooler outlet temperature in the precooling and liquefied mixed refrigerant cycle is reduced to 25°C.

[0033] The feed gas components are 98.68% methane, 0.33% ethylene, 0.27% propane, 0.16% butane, 0.22% isobutane, 0.11% isopentane, 0.11% pentane, and 0.11% nitrogen. The main implementation steps are as follows:

[0034] The qualified pre-treated natural gas (7.9MPag, 25°C) first enters the pre-cooling heat exchanger 1 and flows from bottom to top, after cooling to -60°C, it is extracted and separated into two strands, one of which exchanges heat with the BOG in the LNG stor...

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Abstract

The invention discloses a double-mixed-refrigerant liquefying system applied to a base-load type natural gas liquefying plant. The system comprises a pre-cooling heat exchanger, a liquefying heat exchanger, a pre-cooling mixed refrigerant refrigeration circulation mechanism and a liquefying mixed refrigerant refrigeration circulation mechanism. Due to the fact that the pre-cooling portion adopts mixed refrigerants, the system is high in heat exchange efficiency, few in heat exchanger and simple in flow structure compared with the existing propane pre-cooling process. The pre-cooling heat exchanger and a deep-cooling heat exchanger both adopt a winding pipe type heat exchanger and are good in severe operation working condition adaptability and long in service life. Three-stage throttling is adopted in the pre-cooling and heat-exchange processes and effectively reduces heat exchange power consumption compared with the existing two-stage throttling. Low temperature boil off gas (BOG) directly exchanges heat with raw material gas, so that the system improves heat exchange efficiency compared with the prior art that the BOG is mostly adopted to conduct heat exchange with the refrigerants.

Description

technical field [0001] The invention relates to a double-mixed refrigerant liquefaction system applied to a base-load type natural gas liquefaction plant, and belongs to the technical field of natural gas liquefaction. Background technique [0002] At present, the common domestic natural gas liquefaction technology is mostly nitrogen expansion and single-stage mixed refrigerant cycle refrigeration process, which can only be applied to small-scale LNG plants, usually using plate-fin heat exchangers, which are not highly adaptable to high-pressure gas sources, and The service life is shorter. The liquefaction process used in large-scale natural gas liquefaction plants in foreign countries mostly adopts propane precooling mixed refrigerant liquefaction process (C3 / MR) or dual mixed refrigerant refrigeration liquefaction process (DMR). The former (C3 / MR) precooling heat exchanger usually uses Floating head heat exchangers require a large number of heat exchangers for multi-stre...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): F25J1/02
Inventor 陈杰单彤文黄虎龙花亦怀浦晖罗婷婷程昊高玮
Owner CHINA NAT OFFSHORE OIL CORP